Solenoid drive apparatus

ABSTRACT

In a solenoid driving device of the type in which energy stored in a capacitor is used for re-driving of the solenoid, the generation of heat in the current back-flow preventing circuit that prevents the back-flow of current to the power supply terminal is suppressed, and the generation of heat in the rectifying element through which the current that flows to the capacitor passes is also suppressed. Electric power that is accumulated in the solenoid when the driving of the solenoid is stopped is temporarily stored in a capacitor, and a high voltage that is generated by the charging utilizing the peak voltage of the capacitor is utilized as the power supply for a discharge control circuit that is used to control the discharge of this capacitor. A current back-flow preventing circuit is constructed from a switching element such as an FET or the like, so that the generation of heat in this circuit is suppressed. Furthermore, a rectifying element through which the current that flows to the capacitor passes is constructed from a switching element such as an FET or the like, so that the generation of heat in this element is suppressed.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a solenoid for fuel injection,which is used in an electronically controlled fuel injection device thatsupplies fuel to an engine or the like, and more particularly relates toa solenoid driving device using a system in which the electric powerthat is accumulated in the solenoid when the driving of the solenoid isstopped is temporarily stored in a capacitor, and the electric powerthat is stored in this capacitor is supplied to the solenoid when thesolenoid is again driven.

[0003] 2. Description of the Related Art

[0004]FIG. 8 is a block diagram which shows the construction of a commonsolenoid driving device. This solenoid driving device is constructedfrom a solenoid 11, a solenoid driving element 12 which is used to drivethe solenoid 11, a solenoid driving element control circuit 13 whichcontrols the on/off switching of the solenoid driving element 12 on thebasis of control signals that are input from the outside, and a snubbercircuit 14 that is used to consume the electric power that isaccumulated in the solenoid 11 when the driving of the solenoid 11 isstopped. In FIG. 8, 15 indicates a power supply terminal to which apower supply voltage (battery voltage) V_(B) is applied, and 16indicates a control signal input terminal.

[0005] In the case of the solenoid driving device constructed as shownin FIG. 8, when the solenoid driving element 12 is in an “on” state,current flows through the solenoid 11, and fuel is injected after afixed period of time. After a fixed period of time has elapsed in thisstate, the solenoid driving element 12 is switched to an “off” state inorder to stop the injection of fuel. At this time, the current that hadbeen flowing to the solenoid 11 flows to the snubber circuit 14, and theelectric power is consumed by this snubber circuit 14. As a result, theelectric current that flows to the solenoid 11 is gradually reduced, andeventually reaches zero so that the injection of fuel is stopped.

[0006]FIG. 9 is a circuit diagram which shows the concrete constructionof the solenoid driving device shown in FIG. 8. The solenoid drivingelement 12 is constructed from an N-channel field effect transistor(hereafter referred to as an “FET”) 121. The solenoid driving elementcontrol circuit 13 is constructed from an npn transistor 131 and fourresistors 132, 133, 134 and 135. The snubber circuit 14 is constructedfrom a Zener diode 141.

[0007] One end of the solenoid 11 is connected to the power supplyterminal 15, and the other end is connected to the drain terminal of theFET 121 and the cathode terminal of the Zener diode 141. The sourceterminal of the FET 121 and the anode terminal of the Zener diode 141are grounded. The collector terminal of the npn transistor 131 isconnected to the gate terminal of the FET 121. The first resistor 132 isconnected between this collector terminal and the power supply terminal15. The base terminal of the npn transistor 131 is connected to thecontrol signal input terminal 16 via the second resistor 133. Thecontrol signal input terminal 16 is pulled up to the power supplyvoltage V_(CC) by the third resistor 134. The emitter terminal of thenpn transistor 131 is connected to the base terminal via the fourthresistor 135, and is grounded.

[0008]FIG. 10 is a circuit diagram which shows another example of theconcrete construction of the solenoid driving device shown in FIG. 8. Inthe solenoid driving device shown in FIG. 10, the anode terminal of theZener diode 141 in the device shown in FIG. 9 is connected to thecollector terminal of the npn transistor 131 via a fifth resistor 136instead of being grounded, and a diode 142 is connected between thecathode terminal of the Zener diode 141 and the solenoid 11 so that thisdiode is oriented in the direction in which current flows from thesolenoid 11 to the Zener diode 141.

[0009] However, in the case of the solenoid driving devices constructedas shown in FIGS. 8 through 10, when the capacity of the solenoid 11 isincreased, the electric power that is consumed by the snubber circuit 14is considerably increased, so that the generation of heat becomes aproblem. Accordingly, for the purpose of reducing this generation ofheat and achieving effective utilization of the electric power and anincreased driving speed, a solenoid device with a construction in whichthe energy [that accumulates] when the coil current that flows to thesolenoid is stopped is temporarily stored in a capacitor, and the coilcurrent is abruptly increased by utilizing the energy stored in thecapacitor when the coil current is again caused to flow to the solenoid,is universally known.

[0010]FIG. 11 is a block diagram which shows the construction of aconventional solenoid driving device of the type in which energy storedin a capacitor is utilized in the re-driving of the solenoid. Thissolenoid driving device is constructed from a solenoid 11, a solenoiddriving element 12, a solenoid driving element control circuit 13, acapacitor 21 that temporarily stores the energy that accumulates whenthe driving of the solenoid 11 is stopped, a discharge control element22 that controls the discharge of the capacitor 21, a discharge controlcircuit 23 that controls the on/off switching of the discharge controlelement 22, a DC-DC converter circuit 24 that raises the power supplyvoltage V_(B) and supplies a high voltage to the discharge controlcircuit 23, a current back-flow preventing circuit 25 that prevents thevoltage from entering the power supply side when a high voltage storedin the capacitor 21 is applied to the solenoid 11, and a rectifyingelement 26 that prevents a direct current from flowing into the solenoiddriving element 12 from the capacitor 21 as a result of the high voltagestored in the capacitor 21. Furthermore, constructions that are the sameas in the apparatus shown in FIG. 8 are labeled with the same symbols,and a description is omitted.

[0011] Next, the operation of the solenoid driving device constructed asshown in FIG. 11 will be described. First, when the solenoid drivingelement 12 is switched from an “off” state to an “on” state by thecontrol of the solenoid driving element control circuit 13, a currentbegins to flow to the solenoid 11 from the power supply terminal 15 viathe current back-flow preventing circuit 25. Then, after a fixed periodof time has elapsed, fuel injection is initiated. After another fixedperiod of time has elapsed, the solenoid driving element 12 is switchedto an “off” state in order to stop the injection of fuel. At this time,the current that had been flowing to the solenoid 11 flows to thecapacitor 21 via the rectifying element 26. The voltage VC of thecapacitor 21 rises at the same time that current flows in, so that theelectric power that had accumulated in the solenoid 11 is absorbed bythe capacitor 21. The rise of the voltage VC of the capacitor stops atthe same time that the current flowing into the capacitor 21 reacheszero.

[0012] When fuel injection is again performed following this state, thesolenoid driving element 12 is switched to an “on” state, and at thesame time, the discharge control element 22 is switched to an “on”state. As a result, the voltage VSH on the high-potential side of thesolenoid 11 becomes the same as the voltage VC generated by the chargingof the capacitor 21, and becomes higher than the power supply voltageV_(B) . Accordingly, a current abruptly begins to flow to the solenoid11. Since this current flows out from the capacitor 21, the voltage VCof the capacitor 21, i.e., the voltage VSH on the high-potential side ofthe solenoid 11, drops. Then, at the point in time at which the voltageVSH on the high-potential side of the solenoid 11 becomes lower than thepower supply voltage V_(B) , the current that flows out of the capacitor21 becomes zero, and a current begins to flow to the solenoid 11 fromthe power supply voltage V_(B) . In this case, the current that flows tothe solenoid 11 continues to increase to the voltage that is limited bythe winding resistance of the solenoid 11.

[0013] Thus, excluding the initial fuel injection, the current thatflows to the solenoid 11 is abruptly increased by the voltage that isgenerated by the charging of the capacitor 21 during the second andsubsequent fuel injections. During this abrupt increase, the currentthat flows from the power supply terminal 15 is zero. Accordingly, theamount of current that flows from the power supply terminal 15 isdecreased overall, so that the power consumption is reduced.Furthermore, the current that flows through the solenoid 11 abruptlyrises to a value that is close to the required current; so that theresponse is improved.

[0014] However, in the abovementioned conventional solenoid drivingdevice of the type in which energy stored in capacitor is utilized forre-driving of the solenoid, as is shown in FIG. 11, a DC-DC convertercircuit 24 which is used to supply a high voltage to the dischargecontrol circuit 23 is necessary, resulting in the problem of increasedcomplexity of the circuit and increased size of the circuit.Furthermore, since the current back-flow preventing circuit 25 isordinarily constructed from a diode, the following problem also arises:namely, when a large power supply current flows through this circuit,the amount of heat generated is increased as a result of the voltagedrop of approximately 0.7 V of the diode. Furthermore, since therectifying element 26 between the solenoid driving element 12 and thecapacitor 21 is also constructed from a diode, the generation of heatcaused by the current that flows through this diode is also a problem.

SUMMARY OF THE INVENTION

[0015] The present invention was devised in light of the abovementionedproblems. It is an object of the present invention to provide a solenoiddriving device of the type in which energy stored in a capacitor is usedfor re-driving of the solenoid, wherein a DC-DC converter circuit isunnecessary, and wherein the generation of heat in the current back-flowpreventing circuit that prevents the back-flow of current to the powersupply terminal can be suppressed, and the generation of heat in therectifying element through which the current that flows to the capacitorpasses can be suppressed.

[0016] In order to achieve the abovementioned object, the solenoiddriving device of the present invention is devised so that the electricpower that is accumulated in the solenoid when the driving of thesolenoid is stopped is temporarily stored in a capacitor, and the highvoltage that is generated by the charging utilizing the peak voltage ofthe capacitor is utilized as the power supply of the discharge controlcircuit that is used to control the discharge of the capacitor. In thisinvention, the discharge control circuit is driven by the high voltagethat is generated in the capacitor.

[0017] Furthermore, in the solenoid driving device of the presentinvention, the current back-flow preventing circuit is constructed froma switching element such as an FET or the like. In this invention, thevoltage drop that occurs in the current back-flow preventing circuitwhen current flows from the power supply terminal to the solenoid isreduced, so that the generation of heat in this circuit is suppressed.

[0018] Furthermore, in the solenoid driving device of the presentinvention, the rectifying element through which the current that flowsto the capacitor passes is constructed from a switching element such asan FET or the like. In this invention, the voltage drop that occurs inthe rectifying element when current flows from the solenoid to thecapacitor is reduced, so that the generation of heat in this circuit issuppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a block diagram which shows the construction of asolenoid driving device constituting Embodiment 1 of the presentinvention;

[0020]FIG. 2 is a circuit diagram which shows one example of theconstruction of the solenoid driving device constituting Embodiment 1 ofthe present invention;

[0021]FIG. 3 is a waveform diagram which shows examples of the waveformsin various parts of the solenoid driving device constituting Embodiment1 of the present invention;

[0022]FIG. 4 is a circuit diagram which shows one example of theconstruction of a solenoid driving device constituting Embodiment 2 ofthe present invention;

[0023]FIG. 5 is a circuit diagram which shows one example of theconstruction of a solenoid driving device constituting Embodiment 3 ofthe present invention;

[0024]FIG. 6 is a circuit diagram which shows one example of theconstruction of a solenoid driving device constituting Embodiment 4 ofthe present invention;

[0025]FIG. 7 is a waveform diagram which shows examples of the waveformsin various parts of the solenoid driving device constituting Embodiment4 of the present invention;

[0026]FIG. 8 is a block diagram which shows the construction of a commonconventional solenoid driving device;

[0027]FIG. 9 is a circuit diagram which shows the concrete constructionof the solenoid driving device shown in FIG. 8;

[0028]FIG. 10 is a circuit diagram which shows another example of theconcrete construction of the solenoid driving device shown in FIG. 8;and

[0029]FIG. 11 is a block diagram which shows the construction of aconventional solenoid driving device of the type in which re-driving ofthe solenoid is performed utilizing energy stored in a capacitor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Solenoid driving devices constituting embodiments of the presentinvention will be described in detail below with reference to theattached figures.

[0031]FIG. 1 is a block diagram which shows the construction of asolenoid driving device constituting Embodiment 1 of the presentinvention. This solenoid driving device is constructed from a solenoid31, a solenoid driving element 32, a solenoid driving element controlcircuit 33, a capacitor 34, a power supply terminal 35, a control signalinput terminal 36, a discharge control element 37, a discharge controlcircuit 38, a peak voltage holding circuit 39, a current back-flowpreventing circuit 40, and a rectifying element 41.

[0032] The peak voltage holding circuit 39 holds the peak voltagegenerated by the charging of the capacitor 34, and supplies this voltageto the discharge control circuit 38. Except for the peak voltage holdingcircuit 39, the construction of this solenoid driving device is the sameas that of the conventional solenoid driving device shown in FIG. 11.Furthermore, the operation of this solenoid driving device during thedriving of the solenoid 31 and during the period when this driving isstopped is the same as that of the conventional solenoid driving deviceshown in FIG. 11.

[0033]FIG. 2 is a circuit diagram which shows an example of theconstruction of the solenoid driving device of Embodiment 1 of thepresent invention. This solenoid driving device comprises a solenoid 31,two capacitors 34 and 51, two N-channel FETs 52 and 53, an npntransistor 54, five diodes 55, 56, 57, 58 and 59, a Zener diode 60,eight resistors 61, 62, 63, 64, 65, 66, 67 and 68, a power supplyterminal 35, and a control signal input terminal 36. The first N-channelFET 52 forms the solenoid driving element 32. The second N-channel FET53 forms the discharge control element 37. The first diode 55 forms therectifying element 41. The second diode 56 forms the current back-flowpreventing circuit 40.

[0034] The anode terminal of the second diode 56 is connected to thepower supply terminal 35. The cathode terminal of the second diode 56 isconnected to one end of the solenoid 31. The other end of the solenoid31 is connected to the drain terminal of the first N-channel FET 52 andthe anode terminal of the first diode 55. The source terminal of thefirst N-channel FET 52 is grounded. The cathode terminal of the firstdiode 55 is connected to the positive pole terminal of the firstcapacitor 34. The negative pole terminal of the first capacitor 34 isgrounded. Furthermore, the positive pole terminal of the first capacitor34 is connected to the drain terminal of the second N-channel FET 53.The source terminal of the second N-channel FET 53 is connected to oneend of the solenoid 31 on the side that is connected to the power supplyterminal 35 via the second diode 56.

[0035] Furthermore, the anode terminal of the third diode 58 isconnected to the power supply terminal 35 via the first resistor 61. Thecathode terminal of the third diode 58 is connected to the collectorterminal of the npn transistor 54. The emitter terminal of the npntransistor 54 is grounded. The base terminal of the npn transistor 54 isconnected to the control signal input terminal 36 via the secondresistor 62. The control signal input terminal 36 is pulled up to thepower supply voltage V_(CC) by the third resistor 63. The fourthresistor 64 is connected between the base terminal and emitter terminalof the npn transistor 54. The base terminal of the first N-channel FET52 is connected to the connecting node of the first resistor 61 andthird diode 58 via the fifth resistor 65. The npn transistor 54, firstthrough fifth resistors 61, 62, 63, 64 and 65 and third diode 58constitute the solenoid driving element control circuit 33.

[0036] Furthermore, the anode terminal of the Zener diode 60 isconnected to the power supply terminal 35. The cathode terminal of theZener diode 60 is connected to the positive pole terminal of the firstcapacitor 34 via the sixth resistor 66, and is also connected to theanode terminal of the fourth diode 59. The second capacitor 51 isconnected between the cathode terminal of the fourth diode 59 and thecathode terminal of the second diode 56. The Zener diode 60, sixthresistor 66, fourth diode 59 and second capacitor 51 constitute the peakvoltage holding circuit 39.

[0037] The seventh resistor 67 and eighth resistor 68 are connected inseries between the gate terminal of the second N-channel FET 53 and theconnecting node of the fourth diode 59 and second capacitor 51. Theconnecting node of the seventh resistor 67 and eighth resistor 68 isconnected to the collector terminal of the npn transistor 54. The anodeterminal of the fifth diode 57 is connected to the source terminal ofthe second N-channel FET 53, and the cathode terminal of the fifth diode57 is connected to the gate terminal of the second N-channel FET 53. Thenpn transistor 54, second through fourth resistors 62, 63 and 64,seventh and eighth resistors 67 and 68 and fifth diode 57 constitute thedischarge control circuit 38.

[0038] Characteristic values of the respective elements will be shown asexamples. For example, the respective capacitance values of the firstcapacitor 34 and second capacitor 51 are 100 μF and 0.1 μF. The outputvoltage of the Zener diode 60 is (for example) 9 V. The resistance valueof the first resistor 61 is (for example) 3.3 kΩ. The resistance valueof the second resistor 62 is (for example) 4.7 kΩ. The resistance valuesof the third resistor 63, sixth resistor 66 and seventh resistor 67 are(for example) 10 kΩ. The resistance value of the fourth resistor 64 is(for example) 47 kΩ. The resistance value of the fifth resistor 65 is(for example) 1 kΩ. The resistance value of the eighth resistor 68 is(for example) 2 kΩ.

[0039] The operation of the solenoid driving device constructed as shownin FIG. 2 will be described with reference to FIG. 3. FIG. 3 is adiagram which shows the respective waveforms of voltage VSL on thelow-potential side of the solenoid 31, the voltage VC of the firstcapacitor 34, the voltage VSH on the high-potential side of the solenoid31, and the current I that flows through the solenoid 31.

[0040] First, when the npn transistor 54 is switched from an “on” stateto an “off” state on the basis of a control signal input from thecontrol signal input terminal 36, the first N-channel FET 52 is switchedfrom an “off” state to an “on” state, so that a current begins to flowto the solenoid 31 from the power supply terminal 35 via the seconddiode 56. Then, after a fixed period of time has elapsed, fuel injectionis initiated. In this case, since the second capacitor 51 is notcharged, the second N-channel FET 53 remains in an “off” state.

[0041] After a fixed period of time has elapsed, the npn transistor 54is switched from an “off” state to an “on” state, and the firstN-channel FET 52 is switched to an “off” state. In this case, thecurrent that had been flowing to the solenoid 31 flow to the firstcapacitor 34 via the first diode 55. As a result, the voltage VC of thefirst capacitor 34 rises, and the electric power accumulated in thesolenoid 31 is absorbed by the first capacitor 34. When the currentflowing into the first capacitor 34 reaches zero, the rise of thevoltage VC of the first capacitor 34 simultaneously stops. The secondcapacitor 51 is also charged along with the charging of this firstcapacitor 34. At this point in time, since no current flows to thesolenoid 31, the injection of fuel is stopped.

[0042] When fuel injection is again performed following this state, thenpn transistor 54 is switched from an “on” state to an “off” state, andthe first N-channel FET 52 is switched to an “on” state (time t0 in FIG.3). In this case, since the second capacitor 51 is charged, the gatepotential of the second N-channel FET 53 is at the H level; accordingly,the second N-channel FET 53 is also simultaneously switched to an “on”state. As a result, the voltage VSH on the high-potential side of thesolenoid 31 becomes the same as the voltage VC of the first capacitor34, and thus exceeds the power supply voltage V_(B) . Accordingly, acurrent abruptly begins to flow to the solenoid 31 from the firstcapacitor 34. As a result of the flow of this current, the voltage VC ofthe first capacitor 34, i.e., the voltage VSH on the high-potential sideof the solenoid 31, drops.

[0043] Then, at the point in time where the voltage VSH on thehigh-potential side of the solenoid 31 drops below the power supplyvoltage V_(B) (time t1 in FIG. 3), the current that flows out of thefirst capacitor 34 becomes zero, and a current instead begins to flow tothe solenoid 31 from the power supply terminal 35 via the second diode56. The current that flows to the solenoid 31 in this case continues toincrease to a voltage that is limited by the winding resistance of thesolenoid 31. Fuel injection continues to be performed while a currentflows to the solenoid 31.

[0044] After a fixed time has elapsed in this state, the npn transistor54 is switched from an “off” state to an “on” state. As a result, thefirst N-channel FET 52 is switched to an “off” state (time t2 in FIG.3), and the current that had been flowing to the solenoid 31 flows tothe first capacitor 34 as described above, so that the electric poweraccumulated in the solenoid 31 is stored in the first capacitor 34. Inthis case, the second capacitor 51 is also charged. Then, when thecurrent that flows into the first capacitor 34 reached zero (time t3 inFIG. 3), the injection of fuel stops. When fuel injection is againperformed, the electric power stored in the first capacitor 34 issupplied to the solenoid 31 as described above, and this is repeated.

[0045] In the abovementioned Embodiment 1, when the driving of thesolenoid 31 is stopped, the first capacitor 34 is charged by the currentthat had been flowing to the solenoid 31; as a result, the secondcapacitor 51 of the peak voltage holding circuit 39 is charged, and thesecond N-channel FET 53 of the discharge control element 37 is driven bythe voltage that is generated by this charging of the second capacitor51. Accordingly, there is no need for a DC-DC converter circuit, so thatthe circuit can be simplified, and the size of the circuit can bereduced. Furthermore, a high-performance N-channel FET (second N-channelFET 53), which is less expensive than a P-channel FET, can be used asthe discharge control element 37.

[0046] Embodiment 2

[0047]FIG. 4 is a circuit diagram which shows one example of theconstruction of a solenoid driving device constituting Embodiment 2 ofthe present invention. The solenoid driving device of Embodiment 2differs from Embodiment 1 shown in FIG. 2 in that a switching element isinstalled as the current back-flow preventing circuit instead of thesecond diode 56 that constitutes the current back-flow preventingcircuit 40 of Embodiment 1. There are no particular restrictions on thisswitching element; for example, however, this switching element isconstructed from an N-channel FET (hereafter referred to as the “thirdN-channel FET”) 69.

[0048] Furthermore, in Embodiment 2, an npn transistor (hereafterreferred to as the “second npn transistor”) 70, a third capacitor 71, afifth diode 72 and ninth through twelfth resistors 73, 74, 75 and 76 areinstalled as a switching element control circuit for the purpose ofcontrolling the on/off switching of the third N-channel FET 69. Theremaining construction of Embodiment 2 is the same as that of Embodiment1; accordingly, the same symbols as in Embodiment 1 are assigned, and adescription is omitted.

[0049] The source terminal of the third N-channel FET 69 is connected tothe power supply terminal 35. The drain terminal of the third N-channelFET 69 is connected to the connecting node of the solenoid 31 and thesecond N-channel FET 53. The anode terminal of the fifth diode 72 isconnected to the connecting node of the cathode terminal of the Zenerdiode 60 and the sixth resistor 66. The cathode terminal of the fifthdiode 72 is connected to the anode terminal of the Zener diode 60 (powersupply terminal 35) via the third capacitor 71. The fifth diode 72,third capacitor 71, Zener diode 60 and sixth resistor 66 hold the peakvoltage generated by the charging of the first capacitor 34 in order todrive the switching element control circuit.

[0050] The connecting node of the fifth diode 72 and third capacitor 71is connected to the ninth resistor 73, and this ninth resistor 73 isconnected to the base terminal of the third N-channel FET 69 via thetenth resistor 74. The collector terminal of the second npn transistor70 is connected to the connecting node of the ninth resistor 73 andtenth resistor 74. The emitter terminal of the second npn transistor 70is connected to the power supply terminal 35. The base terminal of thesecond npn transistor 70 is connected to the positive pole terminal ofthe first capacitor 34 via the eleventh resistor 75. The twelfthresistor 76 is connected between the base terminal and emitter terminalof the second npn transistor 70.

[0051] Characteristic values of the respective elements will be shown asexamples. For example, the capacitance of the third capacitor 71 is 0.1μF. The resistance value of the ninth resistor 73 is (for example) 10kΩ. The resistance value of the tenth resistor 74 is (for example) 100Ω. The resistance value of the eleventh resistor 75 is (for example) 20kΩ. The resistance value of the twelfth resistor 76 is (for example) 10kΩ.

[0052] In the solenoid driving device constructed as shown in FIG. 4,the second npn transistor 70 is switched to an “on” state when thevoltage VC of the first capacitor 34 is higher than the power supplyvoltage V_(B) that is applied to the power supply terminal 35; as aresult, the third N-channel FET 69 is switched to an “off” state.Accordingly, the first N-channel FET 52 and second N-channel FET 53 areboth switched to an “on” state, so that when a current abruptly flows tothe solenoid 31 from the first apacitor 34, this current is preventedfrom flowing back toward the power supply terminal 35.

[0053] When the voltage VC of the first capacitor 34 falls below thepower supply voltage V_(B) , the second npn transistor 70 is switched toan “off” state, and the third N-channel FET 69 is switched to an “on”state. As a result, a current flows to the solenoid 31 from the powersupply terminal 35. When the npn transistor 54 of the solenoid drivingelement control circuit 33 is switched to an “on” state in order to stopthe injection of fuel, the second npn transistor 70 is switched to an“on” state, and the third N-channel FET 69 is switched to an “off”state. In this case, the current that flows to the first capacitor 34from the power supply terminal 35 via the solenoid 31 and first diode 55passes through a diode contained in the third N-channel FET 69.

[0054] In the abovementioned Embodiment 2, since there is no need for aDC-DC converter circuit, an effect which makes it possible to simplifythe circuit and reduce the size of the circuit, and an effect whichmakes it possible to use an N-channel FET (second N-channel FET 53) asthe discharge control element 37, are obtained. In addition, since thecurrent back-flow preventing circuit is constructed from a switchingelement, and effect which makes it possible to suppress the generationof heat caused by the current that flows through this circuit isobtained. Furthermore, a high-performance N-channel FET (third N-channelFET 69) which is less expensive than a P-channel FET can be used as theswitching element.

[0055] Embodiment 3

[0056]FIG. 5 is a circuit diagram which shows one example of theconstruction of a solenoid driving device constituting Embodiment 3 ofthe of the present invention. The solenoid driving device of Embodiment3 is devised so that the on/off control of the third N-channel FET 69 inEmbodiment 2 shown in FIG. 4 is performed on the basis of controlsignals (hereafter referred to as “back-flow preventing controlsignals”) that are input from the outside. Furthermore, constructioncomponents that are the same, as in Embodiment 2 are labeled with thesame symbols as in Embodiment 2, and a description of these constructioncomponents is omitted. Only construction components that are differentare described below.

[0057] In Embodiment 2, the base terminal of the second npn transistor70 was connected to the positive pole terminal of the first capacitor 34via the eleventh resistor 75. However, in Embodiment 3, this baseterminal is connected to the terminal into which back-flow preventingcontrol signals are input (the back-flow preventing control signal inputterminal) 77 via the resistor 75. The back-flow preventing controlsignal input terminal 77 is pulled up to the power supply voltage V_(CC)by a thirteenth resistor 78. Furthermore, in Embodiment 3, the emitterterminal of the second npn transistor 70 is grounded.

[0058] Furthermore, a fourteenth resistor 79 and a fifteenth resistor 80are connected in series between the power supply terminal 35 and theground. A terminal (power supply voltage input terminal) 81 which isused to output the power supply voltage to an external control device orthe like is connected to the voltage dividing point. Furthermore, asixteenth resistor 82 and a seventeenth resistor 83 are connected inseries between the positive pole terminal of the first capacitor 34 andthe ground, and a terminal (capacitor voltage input terminal) 84 that isused to output the voltage VC of the first capacitor 34 to an externalcontrol device or the like is connected to the voltage dividing point.Furthermore, the anode terminal of a sixth diode 85 is connected to thesource terminal of the third N-channel FET 69, and the cathode terminalof this sixth diode 85 is connected to the gate terminal of the thirdN-channel FET 69.

[0059] Characteristic values of the respective elements will be shown asexamples. The resistance value of the tenth resistor 74 is (for example)2 kΩ. The resistance value of the eleventh resistor 75 is (for example)4.7 kΩ. The resistance value of the twelfth resistor 76 is (for example)47 kΩ. The resistance value of the thirteenth resistor 78 is (forexample) 10 kΩ. The resistance values of the fourteenth resistor 79 andsixteenth resistor 82 are (for example) 19 kΩ. The resistance values ofthe fifteenth resistor 80 and seventeenth resistor 83 are (for example)1 kΩ.

[0060] In the solenoid driving device constructed as shown in FIG. 5,the second npn transistor 70 is switched to an “on” state and the thirdN-channel FET 69 is switched to an “off” state by an external controldevice or the like when the voltage VC of the first capacitor 34 ishigher than the power supply voltage V_(B) . As a result, the currentthat abruptly flows to the solenoid 31 from the first capacitor 34 isprevented from flowing back toward the power supply terminal 35. Whenthe voltage VC of the first capacitor 34 falls below the power supplyvoltage V_(B) , the second npn transistor 70 is switched to an “off”state, and the third N-channel FET 69 is switched to an “on” state sothat a current flows to the solenoid 31 from the power supply terminal35. The second npn transistor 70 is also switched to an “off” state andthe third N-channel FET 69 is switched to an “on” state when the drivingof the solenoid 31 is stopped in order to stop the injection of fuel, sothat a current flows to the solenoid 31 from the power supply terminal35.

[0061] In the abovementioned Embodiment 3, in addition to an effectwhich makes it possible to simplify the circuit and reduce the size ofthe circuit as a result of the lack of any need for a DC-DC convertercircuit, and an effect which makes it possible to use N-channel FETs 53and 69, the third N-channel FET 69 is also in an “on” state while thefirst capacitor 34 is being charged; accordingly, an effect which makesit possible to suppress the generation of heat in the current back-flowpreventing circuit to an even greater extent than in Embodiment 2 isobtained.

[0062] Embodiment 4

[0063]FIG. 6 is a circuit diagram which shows one example of theconstruction of a solenoid driving device constituting Embodiment 4 ofthe present invention. The solenoid driving device of Embodiment 4differs from Embodiment 3 shown in FIG. 5 in that a switching element isinstalled instead of the first diode 55 that constitutes the rectifyingelement in Embodiment 3. There are no particular restrictions on thisswitching element; for example, however, this switching element isconstructed from an N-channel FET (hereafter referred to as the “fourthN-channel FET”) 86, and the on/off switching of this switching elementis controlled by control signals (hereafter referred to as “capacitorcharging control signals”) that are input from the outside. Furthermore,in Embodiment 4, an npn transistor (hereafter referred to as the “thirdnpn transistor”) 87, a fourth capacitor 88, seventh and eighth diodes 89and 9, a second Zener diode 91 and eighteenth through twenty-thirdresistors 92, 93, 94, 95, 96 and 97 are installed as a switching elementcontrol circuit used to control the on/off switching of the fourthN-channel FET 86. The remaining construction of Embodiment 4 is thatsame as that of Embodiment 3; accordingly, the same symbols as thoseused in Embodiment 3 are assigned, and a description is omitted.

[0064] The source terminal of the fourth N-channel FET 86 is connectedto the connecting node of the solenoid 31 and first N-channel FET 52.The drain terminal of the fourth N-channel FET 86 is connected to thepositive pole terminal of the first capacitor 34. The anode terminal ofthe second Zener diode 91 is connected to the source terminal of thefourth N-channel FET 86, and the cathode terminal of this diode isconnected to the drain terminal of the fourth N-channel FET 86 via theeighteenth resistor 92. The anode terminal of the seventh diode 89 isconnected to the connecting node of the cathode terminal of the secondZener diode 91 and the eighteenth resistor 92. The cathode terminal ofthe seventh diode 89 is connected to the anode terminal of the secondZener diode 91 via the fourth capacitor 88. The seventh diode 89, fourthcapacitor 88, second Zener diode 91 and eighteenth resistor 92 hold thepeak voltage that is generated by the charging of the first capacitor 34in order to drive the switching element control circuit.

[0065] The connecting node of the seventh diode 89 and fourth capacitor88 is connected to the nineteenth resistor 93, and this nineteenthresistor 93 is connected to the base terminal of the fourth N-channelFET 86 via the twentieth resistor 94. The collector terminal of thethird npn transistor 87 is connected to the connecting node of thenineteenth resistor 93 and twentieth resistor 94. The emitter terminalof the third npn transistor 87 is grounded. The base terminal of thethird npn transistor 87 is connected via the twenty-first resistor 95 tothe terminal (capacitor charging control signal input terminal) 98 intowhich capacitor charging control signals are input. The capacitorcharging control signal input terminal 98 is pulled up to the powersupply voltage V_(CC) by the twenty-second resistor 96. The twenty-thirdresistor 97 is connected between the base terminal and emitter terminalof the third npn transistor 87. Furthermore, the anode terminal of theeighth diode 90 is connected to the source terminal of the fourthN-channel FET 86, and the cathode terminal of the eighth diode 90 isconnected to the gate terminal of the fourth N-channel FET 86.

[0066] Characteristic values of the respective elements will be shown asexamples. For example, the capacitance of the fourth capacitor 88 is 0.1μF. The output voltage of the second Zener diode 91 is (for example) 9V. The resistance values of the eighteenth, nineteenth and twenty-secondresistors 92, 93 and 96 are (for example) 10 kΩ. The resistance value ofthe twentieth resistor 94 is (for example) 2 kΩ. The resistance value ofthe twenty-first resistor 95 is (for example) 4.7 kΩ. The resistancevalue of the twenty-third resistor 97 is (for example) 47 kΩ.

[0067]FIG. 7 is a diagram which shows the respective waveforms of thevoltage VSL on the low-potential side of the solenoid 31, the voltage VCof the first capacitor 34, the voltage VSH on the high-potential side ofthe solenoid 31, the current I that flows through the solenoid 31, andthe injector driving pulse, back-flow preventing control signal andcapacitor charging control signal that are input via the control signalinput terminal 36. In the solenoid driving device constructed as shownin FIG. 6, the back-flow preventing control signal is set at the H leveland the second npn transistor 70 is switched to an “off” state by anexternal control device or the like when the voltage VC of the firstcapacitor 34 is higher than the power supply voltage V_(B) . As aresult, the third N-channel FET 69 is switched to an “off” state, sothat the current that abruptly flows to the solenoid 31 from the firstcapacitor 34 is prevented from flowing back toward the power supplyterminal 35.

[0068] When the voltage VC of the first capacitor 34 is lower than thepower supply voltage V_(B) , the back-flow preventing control signal isset at the L level, so that the second npn transistor 70 is switched toan “off” state. As a result, the third N-channel FET 69 is switched toan “on” state, so t that a current flows to the solenoid 31 form thepower supply terminal 35. At the point in time at which the injectordriving pulse is switched from the L level to the H level in order tostop the injection of fuel, the capacitor charging control signal isswitched from the H level to the L level, so that the third npntransistor 87 that was in an “on” state is switched to an “off” state.As a result, the fourth N-channel FET 86 is switched from an “off” stateto an “on” state, so that a current flows to the first capacitor 34.During the charging period of the first capacitor 34, the back-flowpreventing control signal is maintained at the L level, and the thirdN-channel FET 69 is switched to an “on” state, so that a current flowsto the solenoid 31 form the power supply terminal 35. At the point intime at which the charging of the first capacitor 34 is more or lesscompleted, the back-flow preventing control signal and capacitorcharging control signal are returned to the H level, and the third andfourth N-channel FETs 69 and 86 are switched to an “off” state.

[0069] In the abovementioned Embodiment 4, an effect which makes itpossible to simplify the circuit and reduce the size of the circuit isobtained as a result of the lack of any need for a DC-DC convertercircuit. Furthermore, an effect which makes it possible to use N-channelFETs 53 and 69, and an effect which makes it possible to suppress thegeneration of heat in the current back-flow preventing circuit, are alsoobtained. Moreover, since the rectifying element is constructed from aswitching element consisting of the fourth N-channel FET 86, and effectwhich makes it possible to suppress the generation of heat in thiscircuit is also obtained. Furthermore, a high-performance N-channel FET(fourth N-channel FET 86) which is less expensive than a P-channel FETcan be used as the switching element.

[0070] Furthermore, in the abovementioned Embodiments 1 through 4, thecoil current of the solenoid 31 is abruptly increased utilizing theenergy stored in the first capacitor. Accordingly, an effect that allowshigh-speed driving, and that results in a reduced current consumption,can be obtained. Since the current consumption is reduced, thegeneration of heat by the solenoid 31 can be suppressed. When the riseof the coil current is accelerated, the dynamic range as the ratio ofthe time for which fuel is actually injected relative to the injectordriving pulse width is broadened, so that the control of fuel injectionis facilitated. Furthermore, since the current back-flow preventingcircuit is constructed from an FET, the voltage drop in the currentback-flow preventing circuit is approximately 0.1 V, which is smallerthan the voltage drop (0.7 to 1.0 V) in cases where a diode is used;accordingly, the driving voltage of the solenoid is substantiallyincreased, so that an effect that improves the fuel injectionperformance is obtained.

[0071] The present invention is not limited to the abovementionedembodiments; various alterations are possible. For example, theswitching elements that constitute the current back-flow preventingcircuit and the rectifying element are not limited to N-channel FETs;P-channel FETs may also be used. Furthermore, npn or pnp bipolartransistors may also be used. Moreover, the solenoid driving element anddischarge control element are likewise not limited to N-channel FETs;P-channel FETs may also be used, or npn or pnp bipolar transistors maybe used. Furthermore, the present invention can of course be used ininjectors of the conventional type in which fuel that is pressurized andfed by a fuel pump or regulator is injected, and may also be used ininjector devices of a new type in which the injector also acts as a fuelpump, and injects the fuel while pressurizing this fuel. In systems inwhich the injector also acts as a fuel pump, the abovementioned dynamicrange tends to be smaller than in injectors of the conventional type;accordingly, the present invention is especially effective in suchsystems.

[0072] In the present invention, the discharge control circuit is drivenby a high voltage generated in a capacitor. Accordingly, there is noneed for a DC-DC converter circuit, so that the circuit can besimplified and reduced in size. Furthermore, in the present invention,the voltage drop that occurs in the current back-flow preventing circuitwhen current flows from the power supply terminal to the solenoid isreduced, so that the generation of heat in this circuit is suppressed.Moreover, in the present invention, the voltage drop that occurs in therectifying element when current flows from the solenoid to the capacitoris reduced, so that the generation of heat in this element issuppressed.

1. A solenoid driving device comprising: a solenoid for fuel injection;a capacitor which temporarily stores electric power accumulated in saidsolenoid when the driving of said solenoid is stopped, and whichdischarges when said solenoid is again driven, so that said storedelectric power is supplied to said solenoid; a discharge control elementwhich controls the discharge of said solenoid; and a discharge controlcircuit which uses as a power supply a voltage that is generated by thecharging utilizing the peak voltage of said capacitor, and whichcontrols said discharge control element.
 2. The solenoid driving deviceaccording to claim 1, wherein said discharge control element is a fieldeffect transistor.
 3. A solenoid driving device comprising: a solenoidfor fuel injection; a power supply terminal to which a power supplyvoltage is applied; a capacitor which temporarily stores electric poweraccumulated in said solenoid when the driving of said solenoid isstopped, and which discharges when said solenoid is again driven, sothat said stored electric power is supplied to said solenoid; and aswitching element which cuts off said power supply terminal from saidsolenoid when the voltage that is generated by the charging of saidcapacitor is higher than the power supply voltage.
 4. A solenoid drivingdevice comprising: a solenoid for fuel injection; a power supplyterminal to which a power supply voltage is applied; a capacitor whichtemporarily stores electric power accumulated in said solenoid when thedriving of said solenoid is stopped, and which discharges when saidsolenoid is again driven, so that said stored electric power is suppliedto said solenoid; a discharge control element which controls thedischarge of said capacitor; a discharge control circuit which uses as apower supply a voltage that is generated by the charging utilizing thepeak voltage of said capacitor, and which controls said dischargecontrol element; and a switching element which cuts off said powersupply terminal from said solenoid when the voltage that is generated bythe charging of said capacitor is higher than the power supply voltage.5. The solenoid driving device according to claim 3, further comprisinga switching element control circuit which uses as a power supply avoltage that is generated by the charging utilizing the peak voltage ofsaid capacitor, and which controls the on/off switching of saidswitching element.
 6. The solenoid driving device according to claim 3,wherein said switching element is a field effect transistor.
 7. Thesolenoid driving device according to claim 3, wherein said switchingelement is controlled on the basis of control signals that are inputfrom the outside so that the current path between said power supplyterminal and said solenoid is connected when a current flows to saidsolenoid from said power supply terminal.
 8. A solenoid driving devicecomprising: a solenoid for fuel injection; a capacitor which temporarilystores electric power accumulated in said solenoid when the driving ofsaid solenoid is stopped, and which discharges when said solenoid isagain driven, so that said stored electric power is supplied to saidsolenoid; and a switching element which connects the current pathbetween said solenoid and said capacitor when the electric power that isaccumulated in said solenoid when the driving of said solenoid isstopped is stored in said capacitor, and which cuts said solenoid offfrom said capacitor when the electric power that is stored in saidcapacitor is supplied to said solenoid.
 9. The solenoid driving deviceaccording to claim 8, wherein said switching element is a field effecttransistor.
 10. A solenoid driving device comprising: a solenoid forfuel injection; a power supply terminal to which a power supply voltageis applied; a capacitor which temporarily stores electric poweraccumulated in said solenoid when the driving of said solenoid isstopped, and which discharges when said solenoid is again driven, sothat said stored electric power is supplied to said solenoid; adischarge control element which controls the discharge of saidcapacitor; a discharge control circuit which uses as a power supply avoltage that is generated by the charging utilizing the peak voltage ofsaid capacitor, and which controls said discharge control element; afirst switching element which cuts off said power supply terminal fromsaid solenoid when the voltage that is generated by the charging of saidcapacitor is higher than the power supply voltage; and a secondswitching element which connects the current path between said solenoidand said capacitor when the electric power that is accumulated in saidsolenoid when the driving of said solenoid is stopped is stored in saidcapacitor, and which cuts said solenoid off from said capacitor when theelectric power that is stored in said capacitor is supplied to saidsolenoid.
 11. The solenoid driving device according to claim 10, whereinsaid second switching element is a field effect transistor.
 12. Thesolenoid driving device according to claim 4, further comprising aswitching element control circuit which uses as a power supply a voltagethat is generated by the charging utilizing the peak voltage of saidcapacitor, and which controls the on/off switching of said switchingelement.
 13. The solenoid driving device according to claim 4, whereinsaid switching element is a field effect transistor.
 14. The solenoiddriving device according to claim 5, wherein said switching element is afield effect transistor.
 15. The solenoid driving device according toclaim 4, wherein said switching element is controlled on the basis ofcontrol signals that are input from the outside so that the current pathbetween said power supply terminal and said solenoid is connected when acurrent flows to said solenoid from said power supply terminal.